1. Field of the Invention
The present general inventive concept relates to an image forming apparatus and image forming method, and more particularly, to a multi-beam image forming apparatus and a method of forming an image using the same.
2. Description of the Related Art
An image forming apparatus such as a laser printer, a digital copier, etc., includes a laser scanning unit to emit a laser beam that forms an electrostatic latent image on a photosensitive body.
The laser beam emitted from a semiconductor laser located in the laser scanning unit is reflected by a polygonal mirror onto a photosensitive body moving with a predetermined speed. As the polygonal mirror rotates, the reflected laser beam scans a direction (main-scanning direction) perpendicular to the moving direction (sub-scanning direction) of the photosensitive body. The laser beam is modulated corresponding to the input image so that the corresponding electrostatic latent image is formed on the photosensitive body.
Recently, a multi-beam image forming apparatus using a light scanning unit having a plurality of laser beams has been developed in order to increase the printing speed. When the light scanning unit includes only one laser beam, one main-scanning line is formed on the photosensitive body during the scanning process in the sub-scanning direction. When the light scanning unit includes a plurality of laser beams, the laser beams form a plurality of lines on the photosensitive body during the scanning process in the sub-scanning direction. Therefore, the printing speed of the multi-beam image forming apparatus is much higher than that of a single beam image forming apparatus. An example of the multi-beam image forming apparatus is disclosed in Korean Patent Laid-open Publication No. 1999-49598.
In addition to increasing the printing speed, various methods for improving resolution using a multi-beam image forming apparatus have been proposed. A multi-beam image forming apparatus for improving resolution is disclosed in Japanese Patent Laid-open Publication No. 2004-223754, entitled “Image Forming Apparatus”, filed by Tsuruya. According to Tsuruya, overlapping laser beams are applied sequentially in different main-scanning directions. The respective laser beams are scanned onto the photosensitive body in a dot shape having a certain size, and the dots overlap to thereby improve resolution.
However, it is difficult to precisely control the time intervals between scanning in different main-scanning directions with the plurality of laser beams. The printing speed decreases when this method is used to improve the resolution, since it is time-consuming for the plurality of laser beams to be scanned to form one main-scanning line,